Beta-eudesmol, a
sesquiterpenoid isolated from "So-jutsu" (Atractylodis lanceae rhizomas), is known to have various unique effects on the nervous system. We examined in detail the mechanism by which
beta-eudesmol modified neuronal function using rat
pheochromocytoma cells (PC-12).
Beta-eudesmol at concentrations of 100 and 150 microM significantly induced neurite extension in PC-12 cells, which was accompanied, at the highest concentration, by suppression of [(3)H]
thymidine incorporation.
Beta-eudesmol at concentrations of 100 and 150 microM also evoked a significant increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) in these cells, as determined by the
fura 2 assay. Much of this increase remained even after the extracellular Ca(2+) was chelated by
EGTA. The [Ca(2+)](i) increase induced by
beta-eudesmol was partially inhibited by the
phosphoinositide-specific
phospholipase C (PI-PLC) inhibitor 1-[6-[[17beta-methoxyestra-1,3,5(10)-
trien-17-yl]amino]hexyl]-1H-
pyrrole-2,5-dione (U-73122) (2 microM) under extracellular Ca(2+)-free conditions. Furthermore,
beta-eudesmol, in a concentration-dependent fashion, caused an accumulation of
inositol phosphates.
beta-Eudesmol (150 microM) promoted phosphorylation of both
mitogen-activated protein kinase (MAPK) and cAMP-responsive
element binding protein in a time-dependent manner. These phosphorylations were suppressed by the
MAPK kinase inhibitor 2-(2'-amino-3'-methoxyphenol)-oxanaphthalen-4-one (
PD98059) (50 microM),
U-73122 (2 microM), the
calmodulin inhibitor
N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (
W7) (1-10 microM), and the
protein kinase A inhibitor N-[2-(4-bromocinnamylamino)ethyl]-5-
isoquinoline (
H89) (1-10 microM).
Beta-eudesmol-induced neurite extension was significantly inhibited by both
U-73122 (2 microM) and
PD98059 (30 microM), suggesting the involvement of PI-PLC and MAPK in neurite outgrowth.
Beta-eudesmol, being a small molecule, may therefore be a promising lead compound for potentiating neuronal function. Furthermore, the
drug may be useful in helping to clarify the mechanisms underlying neuronal differentiation.